In order not to unnecessarily extend the pedal travel for braking a vehicle with worn linings, it is known to provide automatically acting adjusting devices in which the initial position of the brake piston readjusts itself automatically depending on the brake lining's wear. Such adjusting devices can be furnished with a thread without self-locking engagement as described in more detail for instance in German published patent application 38 02 014.
The situation occurs in automatic adjusting devices of this type that the piston has moved relatively far from its initial position when the worn linings are replaced. To obtain space for fitting the new linings, it has been known to restore the piston to its initial position by virtue of resetting means. Such resetting means is known for example from German published patent applications 37 13 201, 18 13 560 and from German patent 16 75 245. It is a shortcoming in the known resetting means that either a threaded spindle is supported relative to the housing to be rotationally fixed, or the known adjusting devices are equipped with a non-reversible thread between nut and threaded spindle. From both measures ensues the disadvantage that either the piston must be screwed down to its initial position by a threaded spindle movement, or that the screw must be turned about its longitudinal axis on its end remote from the piston by means of a special drive in order to restore the piston into its initial position.